Several standard protocols for wireless local area networks, commonly referred to as WLANs, are becoming popular. These include protocols such as 802.11 (as set forth in the 802.11 wireless standards), home RF, and Bluetooth. The standard wireless protocol with the most commercial success to date is the 802.11b protocol.
While the specifications of products utilizing the above standard wireless protocols commonly indicate data rates on the order of, for example, 11 MBPS and ranges on the order of, for example, 100 meters, these performance levels are rarely, if ever, realized. Performance shortcomings between actual and specified performance levels have many causes including attenuation of the radiation paths of RF signals, which are typically in the range of 2.4 GHz in an operating environment such as an indoor environment. Base or AP to receiver or client ranges are generally less than the coverage range required in a typical home, and may be as little as 10 to 15 meters. Further, in structures having split floor plans, such as ranch style or two story homes, or those constructed of materials capable of attenuating RF signals, areas in which wireless coverage is needed may be physically separated by distances outside of the range of, for example, an 802.11 protocol based system. Attenuation problems may be exacerbated in the presence of interference in the operating band, such as interference from other 2.4 GHz devices or wideband interference with in-band energy. Still further, data rates of devices operating using the above standard wireless protocols are dependent on signal strength. As distances in the area of coverage increase, wireless system performance typically decreases. Lastly, the structure of the protocols themselves may affect the operational range.
One common practice in the mobile wireless industry to increase the range of wireless systems is through the use of repeaters. However, problems and complications arise in that system receivers and transmitters may operate at the same frequency in a WLAN utilizing, for example, 802.11 or 802.16 WLAN wireless protocol. In such systems, when multiple transmitters operate simultaneously, as would be the case in repeater operation, difficulties arise. Other problems arise in that, for example, the random packet nature of typical WLAN protocols provides no defined receive and transmit periods. Because packets from each wireless network node are spontaneously generated and transmitted and are not temporally predictable packet collisions may occur. Some remedies exist to address such difficulties, such as, for example, collision avoidance and random back-off protocols, which are used to avoid two or more nodes transmitting packets at the same time. Under 802.11 standard protocol, for example, a distributed coordination function (DCF) may be used for collision avoidance.
Such operation is significantly different than the operation of many other cellular repeater systems, such as those systems based on IS-136, IS-95 or IS-2000 standards, where the receive and transmit bands are separated by a deplexing frequency offset. Frequency division duplexing or multiplexing, (FDD or FDM), operation simplifies repeater operation since conflicts associated with repeater operation, such as those arising in situations where the receiver and transmitter channels are on the same frequency, are not present.
Other cellular mobile systems separate receive and transmit channels by time rather than by frequency and further utilize scheduled times for specific uplink/downlink transmissions. Such operation is commonly referred to as time division duplexing or multiplexing, e.g. TDD or TDM. Repeaters for these systems are easily built, as the transmission and reception times are well known and are broadcast by a base station. Receivers and transmitters for these systems may be isolated by any number of means including physical separation, antenna patterns, or polarization isolation.
Thus, WLAN repeaters operating on the same frequencies with, for example, TDD but no scheduling are presented with unique constraints due to the spontaneous transmission capabilities of network nodes and therefore require a unique solution. Further, in cases where uplink and downlink times are known, repeaters configured to ignore schedule information may be less costly to build. Thus some form of isolation must exist between the receive and transmit channels of WLAN repeaters using the same frequency for both channels. While some related systems such as, for example, CDMA systems used in wireless telephony, achieve channel isolation using sophisticated techniques such as directional antennas, physical separation of the receive and transmit antennas, or the like, such techniques are not practical for WLAN repeaters in many operating environments such as in the home where complicated hardware or lengthy cabling is not desirable or may be too costly.
One system, described in International Application No. PCT/US03/16208 and commonly owned by the assignee of the present application, resolves many of the above identified problems by providing a repeater which isolates receive and transmit channels using a frequency detection and translation method. The WLAN repeater described therein allows two WLAN units to communicate by translating packets associated with one device at a first frequency channel to a second frequency channel used by a second device. The direction associated with the translation or conversion, e.g. from the frequency associated with the first channel to the frequency associated with the second channel, or from the second channel to the first channel, depends upon a real time configuration of the repeater and the WLAN environment. The WLAN repeater may be configured to monitor both channels for transmissions and, when a transmission is detected, translate the received signal at the first frequency to the other channel, where it is transmitted at the second frequency.
The above described approach solves both the isolation issue and the spontaneous transmission problems as described above by monitoring and translating in response to packet transmissions and may further be implemented in a small inexpensive unit. However, due to requirements associated with the WLAN protocols, the effectiveness of the previously mentioned solution may be limited. For example, the IEEE 802.11 standard requires that an access point transmit a channel identifier indicating the channel upon which the AP is communicating in a protocol message commonly referred to as a beacon. The frequency translating repeater in the above identified application retransmits the beacon on a different channel from the original AP channel. In addition, packets from the AP are transmitted on the same channel as the translated beacon, e.g. the translated frequency. Problems arise in that the beacon identifies that associated packets are being transmitted on the original AP transmission frequency and not the translated frequency. A client unit receiving the beacon may switch to the original AP transmission frequency contained in the beacon and miss packets sent by the repeater on the translated frequency or may discard the beacon preventing a client from connecting.